Scraped surface heat exchangers are in wide use in industry, for example in the processing of foodstuffs. A scraped surface heat exchanger generally includes a long cylindrical outer tube having a material inlet at one end and a material outlet at the other end. A central drive shaft extends inside the outer tube and is coaxial with the outer tube and is driven to rotate inside the outer tube. An annular space between the outer tube and central drive shaft receives the material, such as a foodstuff, which is pumped in the inlet and allowed to travel the length of the tube and escape out the outlet at the other end of the outer tube. Heating or cooling is generally provided to the outer tube so that material changes temperature as it traverses the length of the scraped surface exchanger. Further, radially extending paddles, also referred to as blades, are hingedly connected to the central drive shaft in order to help mix the material and/or scrape the inside surface of the outer tube to prevent material buildup.
In one known way of mounting the blades to the tube, the blade is in the form of a generally rectangular relatively thin flat blade member, with a scraping edge along one side, and an opposed hinge side which is hingedly connected to the drive shaft by means of pins. The pins are items welded onto the drive shaft and generally have a narrow protruding finger as well as an opposed wider finger. The thickness of the blade is dimensioned to slide between the two figures of the pin at an installation angle, and a hole is provided in the blade to which the inner finger can pass through. After the blade is inserted at the installation angle, it is pivoted to a much more shallow angle more tangential with drive shaft, at which point the inner finger protrudes through the hole in the blade thereby restraining the blade from lateral movement and permitting only angular movement. A blade typically has two such mounting connections, i.e., two pin receiving holes. The shaft is provided with pins at appropriate locations so that each blade is typically restrained by two, or sometimes more, of these hinged pin connections.
The blades are generally installed on the drive shaft in this manner at a time when the drive shaft is removed from the outer tube of the scraped surface heat exchanger. Installation occurs not only at initial setup, but also after each cleaning cycle of the device, which can occur frequently. During insertion of the drive shaft into the scraped surface heat exchanger tube, it is desirable that the blades remain at the shallow angle so that the fingers are protruding through the holes in the blades and the blades are retained in place during installation. Further, the blades need to be held at their relatively shallow angle during installation so that they fit within the diameter of the outer tube and the drive shaft can be slid into the outer tube.
In the case of a horizontally and vertically arranged scraped surface heat exchanger, this practice may be somewhat cumbersome and require tying strings around the blades to hold the blades in, or may be accomplished by the user holding the blades in with their hands as the drive shaft is inserted into the outer tube.
Due to the length of a drive tube, there are typically several blades arranged at regular intervals longitudinally along a single drive shaft. Also, the blades are generally arranged with four blades, each at a 90° angle to each other, around the circumference of the drive tube, at each blade location.
It would be apparent that if the blades are permitted to swing outwardly to their installation position, depending on their orientation, they may be able to freely slide away from the pin, since the inner finger is not restraining them by engagement with the hole in the blade. This problem becomes even more severe in the case of a vertically arranged scraped surface heat exchanger. In order to permit a shaft, which in some instances may be 7-8 feet long, to fit within a tube of the same length, it is known to mount the tubes quite high above the floor surface, and insert the drive shaft using a hydraulic lift controlled by a manually actuated lever at the floor level. With a vertically oriented tube in this configuration, during installation if the blades swing out to their installation angle position, they will then fall freely downward, which is undesirable and requires the operator to reposition them again before proceeding.
Accordingly, is would be desirable to have a method and apparatus to facilitate the mounting of a scraped surface heat exchanger blade onto a drive shaft, while still using a pin type connection.